I have this heavy steel Hercules frame. It rides on a sturmey archer 3-speed coaster hub. I've got ideas on how I can make this the loaded touring dream machine I'll pedal to the ends of the earth. I just need to know if these ideas are valid.

Your pics aren't coming up.
Your current stated wheel size, 26x1 3/8" is probably ETRTO 590 mm, or possibly 597 mm. 700C wheels are ETRTO 622 mm. Means a 700C rim will sit 16 mm higher up than your current rims. There will probably be issues with brake reach, maybe even fender clearance.
For touring I don't see the point in deliberately avoiding a coaster brake. Sure, coasters can overheat on long descents, but there are no issues with combining a coaster brake with rim braking. Might even be a nice redundancy feature on a tourer.
If you find a fork with lowrider eyelets, it's probably not a "road" fork as such. The presence of rack mounts is a pretty good indicator that its intended usage was touring already to start with.

Personally I find the combo of a riser stem and a drop bar kinda contrary, but it is used every now and then on tourers. Me, I'd go with a trekking bar instead. Of course, it'd depend on where your bar end up in relation to the saddle.
26x1 3/8" is a so-so touring choice due to accessibility of spares. If you'd stick with the 700C or the most common 26"(559mm) size you'd be able to pick up a new tire of some sort just about anywhere. Should you need a whole new wheel, it's readily within reach as well.
26x1 3/8" spares will be not be quite as easy. Not impossible though.
The recently revived 650B standard might get you out of any brake reach issues. Don't know how spares would compare to 26x1 3/8" though.
The advantages of disc brakes are shining clearer and clearer every year. Particularly the mechanical ones have proven to be very robust, braking is pretty much unaffected by rain, and you can ride in dust and dirt to your heart's content w/o ever wearing out the rims.
Particularly for loaded touring I'd certainly want more than 3 gears. There's no way I'd be happy with having to cover that potential speed range with only 3 gears.

Oh, and, you have some skilled Frame-builders in Philly, to take a torch to the fork and repair it,
or replicate and improve it for your new requirements,
add fittings to mount a front load carrying system , and light bracket. and Etc.